Cationization of protein antigens. II. Alteration of regulatory properties

Immunoregulatory effects of cationized bovine serum albumin (cBSA) and native bovine serum albumin (nBSA) have been investigated. Intravenous administration of nBSA to BDF1 mice substantially suppressed the antibody response to subsequent immunization with either nBSA or cBSA, whereas pretreatment with cBSA by the same route significantly enhanced the responses to both antigens. The functional properties of BSA-specific T and B cells from mice immunized with cBSA or nBSA were examined in reconstitution experiments in which splenic T populations together with B cells were transferred into irradiated syngeneic recipients. Transfer of splenic T cells from mice primed with nBSA caused profound suppression of the response to subsequent immunization with nBSA or cBSA, whereas transfer of either B or T cells from cBSA treated mice produced an enhanced response to both antigens. C57BL/6 mice, which are considered to be low responders to BSA, produced a significant antibody response to BSA when immunized with cBSA. In contrast, immunization with nBSA did not produce measureable amounts of antibody in mice of this strain. Our data clearly demonstrate that cationized BSA exhibits unique immunogenic properties due to alterations in the self-regulation of the immune response.     

Cationization of protein antigens. I. Alteration of immunogenic properties

We have shown that a cationized form of bovine serum albumin (BSA) produced by substituting anionic side chain carboxylic groups with aminoethylamide groups possesses unique immunologic properties. The two forms of antigen, native (nBSA) and cationized (cBSA), cross-react at the level of the B cell, as evidenced by the ability of antibody raised against one form to react with the other and by inhibition assays using ELISA. T cell cross-reactivity was also observed in proliferation assays, but the amount of cBSA required for stimulation was 500 times less than the amount of native protein needed. In vivo, cBSA produced responses which, at their optimal levels, were at least double the response to nBSA and which showed a different kinetic pattern, peaking later and lasting longer than the response to the native molecule. Moreover, antibodies were produced in response to administration of cBSA but not nBSA when given i.v. in saline, without an adjuvant. Although a mechanism for these phenomena is not yet clear, we speculate that the cBSA may have a greater affinity for antigen-presenting cells or for the T cell receptor, or that the altered structure may enhance recognition of the molecule by APC and/or helper T cells.     

Cationization of protein antigens. V. Effect of the degree of cationization on patterns of immune responsiveness.

Preparations of bovine serum albumin (BSA) were cationized by substituting anionic side chain carboxyl groups with polycationic aminoethylamide groups. Different degrees of substitution were obtained by varying the reaction time. Mice immunized with partially cationized proteins produced early increased levels of antibody over those made by mice immunized with nBSA, followed by a period of decreased response before returning to a second period of enhanced and prolonged antibody synthesis. In contrast, fully substituted BSA gave rise to a significantly enhanced response which was delayed in its onset. Differences in isotype or in antibody specificity during the early and late periods of enhanced responsiveness could not be demonstrated. Cell transfer experiments showed that T cells harvested from mice immunized with the less cationized cBSA preparations could, in contrast to T cells from mice immunized with the fully cationized preparations, suppress antibody responses to both nBSA and cBSA in normal mice. These data are consistent with the possibility that the partially cationized proteins, in contrast to the fully cationized antigen, yield a unique pattern of responsiveness due to retention of determinants necessary for the induction of Ts while exhibiting the enhanced immunogenicity characteristic of cationized molecules.     

Cationization of protein antigens. IV. Increased antigen uptake by antigen-presenting cells

Cationization of BSA generates a molecule that mounts antibody responses of increased magnitude and duration and induces T cell proliferation at concentrations 500 times less than native BSA (nBSA). To explain the alteration in immunogenic properties of this Ag, the uptake of nBSA and cationized BSA (cBSA) by splenic APC has been investigated. T cell proliferation assays were conducted with nBSA and cBSA preparations with varying degrees of substitution. An inverse correlation between the degree of cationization and the amounts of Ag needed for optimal T cell reactivity was observed. To determine whether affinity for APC resulted in an increased uptake of cBSA, splenic APC were incubated with nBSA or cBSA for varying amounts of time. Comparisons were made at each time point between untreated Ag-pulsed APC (Ag uptake) and paraformaldehyde-fixed Ag-pulsed APC (processed Ag). Proliferation of T cells primed with nBSA or cBSA increased in proportion to the amount of time of APC exposure to high concentrations of nBSA, first appearing after a 2-h pulse and peaking at 8 h. Conversely, untreated APC needed only a 30-min cBSA exposure to induce either nBSA- or cBSA-primed T cell proliferation, indicating a rapid uptake of cBSA. Comparisons with proliferation induced by paraformaldehyde-fixed cBSA APC indicate that nBSA T cells recognize a lag phase-processed form of cBSA, whereas a majority of cBSA T cells recognize either a rapidly processed form of cBSA, or a membrane-processed cBSA molecule without a classical lag phase processing event. When monensin was used as an inhibitor of fluid phase pinocytosis in splenic APC, the presentation of nBSA was inhibited by 85%, but the presentation of cBSA was inhibited by only 20%. These results imply that nBSA enters the cell by fluid phase pinocytosis, whereas cBSA enters by a nonspecific adsorptive mechanism. The different modes of cellular entry for the two molecules, nBSA and cBSA, resulting in a rapid uptake of cBSA, may have important ramifications on T cell activation and immunoregulation.     

Identification of macrophage cell-surface binding sites for cationized bovine serum albumin.

Autoimmune diseases are characterized by the presence of autoantibodies often restricted to host proteins exhibiting charge rich domains. Charged polypeptides elicit strong immune responses, and cationized bovine serum albumin and other cationic proteins are significantly more immunogenic than their less charged counterparts. These phenomena may involve enhanced protein uptake by macrophages, resulting in greater processing and presentation of antigenic peptide-MHC complexes to T-cells. We compared macrophage cell-surface binding and uptake of native and cationized bovine serum albumin. Specific binding of [125I]cationized bovine serum albumin to THP-1 macrophages in vitro was 11-16 fold greater than for native albumin. Half-maximal inhibition of [125I]cationized albumin binding was observed at 10-7M ligand. The specificity of [125I]cationized bovine serum albumin binding and uptake was further studied in terms of competitive inhibition of proteolysis by proteins of varying charge content. Cationized bovine serum albumin, but not native albumin, inhibited proteolysis of [125I]cBSA. Calf thymus histones also inhibited cBSA degradation. High concentration of myelin basic protein was moderately effective at blocking cBSA degradation, while myoglobin and beta lactalbumin showed no inhibition. These results indicate that specific cell-surface binding sites which occur on macrophages may mediate selective uptake of certain proteins with highly charged domains including some autoantigens.     

Cationization of protein antigens. VI. Effects of cationization on the immunoregulatory properties of a bovine serum albumin peptide, a.a. 506-589.

Cationization of bovine serum albumin (BSA) causes a profound increase in its immunogenicity. To establish if immunoregulatory properties of an immunosuppressive peptide are affected by cationization, a BSA peptide, a.a. 506-583, was cationized and tested for its immunogenic properties. A greatly reduced amount of cationized peptide compared to native peptide was required to stimulate BSA-primed T cells to proliferate in vitro. Mice primed with the cationized peptide administered with an adjuvant responded with a significantly greater anti-BSA response than mice immunized with the native form of the peptide. In the absence of an adjuvant i.v. or i.p. administration of the native peptide was immunosuppressive, while the cationized form was immunoenhancing. Both forms of the peptide stimulated in vivo induction of L3T4+ (CD4), and Lyt-2+ (CD8) T cells. Removal of Lyt-2+ T cells from lymph node cultures following immunization with the native peptide caused a significant increase in the proliferation of the remaining T cells. This increase was not observed when the mice were immunized with the cationized peptide. No major BSA B cell determinants were present within the peptide sequence. Mice immunized with the peptide exhibited a negligible anti-BSA antibody response compared to those immunized with the whole BSA molecule. Furthermore, the peptide did not inhibit anti-BSA antibody binding to BSA. We demonstrated that cationization modifies immunoregulatory properties of an immunosuppressive BSA-derived peptide.     

Hierarchy of T cell dependency in antibody response among different antigens.

T cell dependency of antibody response to polyvinylpyrrolidone (PVP), sheep red blood cells (SRBC), bovine gamma globulin (BGG), and bovine serum albumin (BSA) was examined. PVP and the other three are known as a T cell-independent antigen and T cell-dependent antigens respectively. Adult mice were thymectomized, X-irradiated, reconstituted with syngeneic bone marrow cells (TxXB mice), with bone marrow cells plus thymus cells (TxXBT mice), or with bone marrow cells treated with anti-Thy-1.2 serum and complement (TxXB-theta mice) and used as experimental animals. The anti-PVP response of TxXBT mice was significantly lower than that of TxXB mice, suggesting that T cells exerted a suppressive effect on the response to PVP. Both IgM and IgG responses to SRBC and BGG occurred even in TxXB-theta mice with the aid of bacterial lipopolysaccharide (LPS). However, a significant response to BSA was not observed in TxXB mice even in the presence of LPS or several other adjuvants. These results indicate that the T cell dependency of antigens is different among so called thymus-dependent antigens, that antibody response less dependent on the helper action of T cells can be supported by LPS in the absence of T cells, and that anti-BSA response seems to be extremely T cell dependent.     

Experimental model of membranous nephropathy in mice: sequence of histological and biochemical events

An experimental model of membranous nephropathy (MN) has not been established fully in mice. We characterized the time course of MN in a murine MN model induced by cationic bovine serum albumin (cBSA). Preimmunized mice received cBSA intravenously for six weeks to induce MN and were then sacrificed at different times. Metabolic profiles, renal histopathology, lymphocyte subsets, serum anti-cBSA immunoglobulins (Igs), antibody subclasses and circulating immune complexes (CIC) were evaluated to study the severity and mechanisms of disease initiation and progression. Clinical symptoms of overt proteinuria, hypoalbuminaemia and hypercholesterolaemia were observed from week 4, and typical histological findings of diffuse thickening of the glomerular basement membrane and subepithelial deposition were identified after week 6. Granular fluorescent staining for IgG and complement C3 were observed as early as week 4. Total splenocyte number increased, but the percentages of CD4+ and CD8+ cells did not change as the disease progressed. The predominant isotype of anti-cBSA Igs was IgG1, suggesting a T-helper 2 cell-prone immune response in the development of MN. The strong positive immunofluorescent staining of the immune complex concomitant with higher concentrations of Igs in serum but no significant change in CIC levels before week 4 suggest the involvement of in situ deposition of immune complex in the process of MN. This murine model resembles the clinical and pathological features of human MN and may provide a tool for investigating MN; this model may also have potential applications in gene-knockout or transgenic mouse technologies.     

Modulation of humoral immune response by ascorbic acid in Oreochromis mossambicus (Peters).

Fish were treated with sublethal doses of ascorbic acid before being immunised with different physical forms of bovine serum albumin (BSA). Ascorbic acid elevates the antibody response to all the physical forms of BSA tested. Generally, there was an inverse relationship between the dose of ascorbic acid and antibody response. In fish administered with multiple doses of ascorbic acid, no significant enhancement of antibody response was observed.     

沙丁胺醇人工抗原的合成及抗体制备

沙丁胺醇是一种β-兴奋剂,常被很多畜禽水产养殖户非法用于动物养殖。为建立沙丁胺醇在食品中残留的快速检测方法,研究了沙丁胺醇免疫原的合成和抗体的制备方法。采用对氨基苯甲酸法合成了沙丁胺醇（SAL）免疫原SAL-cBSA,采用重氮化法合成的克伦特罗（CL）偶合物CL-cOVA作为包被抗原,用紫外光谱法分析了所合成免疫原和包被抗原。用免疫原SAL-cBSA免疫新西兰大白兔获得多克隆抗体,抗体效价达到32000。采用间接ELISA法检测抗体IC50值为8.79ng/ml,SAL的浓度在1ng/ml~100ng/ml区间时,SAL与对抗体的竞争结合力呈直线关系。表明所制备的沙丁胺醇免疫原具有良好的免疫原性,所制备的抗体拥有很高的灵敏度。     

Experimental Mycoplasma pulmonis infection of rats suppresses humoral but not cellular immune response

Humoral antibody response to sheep red blood cells and cellular immune response to bovine serum albumin were studied in Mycoplasma pulmonis infected, adult, male Sprague-Dawley rats. The hemagglutinating antibody response to sheep red blood cells was evaluated at 0, 3, 5, 7, 14, 21 and 28 days postinfection. Antibody titers during all days postinfection were depressed significantly (p less than 0.05) in infected rats as compared to noninfected controls. Cellular immune responses were evaluated by a delayed hypersensitivity response. Rats were sensitized at 0, 3, 5, 7, 14, 21 or 28 days postinfection with bovine serum albumin and challenged with heat aggregated bovine serum albumin 7 days later. Cell-mediated immune responses in infected rats were not significantly different at any point from controls. These results indicate that M. pulmonis infection in rats suppresses the humoral antibody response to sheep red blood cells, but not the cellular immune response to bovine serum albumin.     

Effect of concanavalin A on lymphocyte interactions involved in the antibody response to type III pneumococcal polysaccharide. II. Ability of suppressor T cells to act on both B cells and amplified T cells to limit the magnitude of the antibody response.

When administered 2 days after immunization with 0.5 microgram Type III pneumococcal polysaccharide (SSS-III), the T lymphocyte mitogen concanavalin A (Con A) stimulates a 2.6-to 7-fold enhancement of the plaque-forming cells (PFC) response to SSS-III in vivo. This enhancement requires the presence of amplified T cells, which act by driving PFC or their precursors to extra rounds of proliferation. The extra proliferation that can be stimulated by Con A is not seen in the normal primary response to SSS-III; but treatment with anti-lymphocyte serum (ALS) to remove suppressor T cells will permit the additional proliferation to occur. This indicates that in the primary response to SSS-III, suppressor T cells act on amplifier T cells to limit the magnitude of the antibody response. Only suppression of B cells can account for the further suppression induced by Con A given at the time of immunization or by low-dose paralysis of the SSS-III response. The relatively late development of amplified activity compared to suppressor activity appears to account for the absence of amplifier activity after primary immunization with SSS-III. It is apparent that one can explain the regulatory effects observed during the development of an immune response to SSS-III only by considering both T cell- B cell and T cell- T cell interactions, together with the temporal relationships involved in those interactions.     

Joint inflammation in mice induced by a MT4+ Lyt-2- T cell clone. Characteristics and the induction of flare-up reactions

Joint inflammations were induced in mice by cloned MT4+ Lyt-2- T cells specific for methylated bovine serum albumin. This was done either by intra-articular or by i.v. administration of the cloned T cells, together with local injection of the antigen. Local rechallenge with methylated bovine serum albumin several weeks after waning of the joint inflammation caused a flare-up reaction. The inflammations were quantified by a 99mTc-uptake method and examined histologically. The arthritis induced by the cloned T cells showed aspects of a delayed type hypersensitivity reaction characterized by an intense infiltrate which resembles the inflammation in the human rheumatoid joint. The data presented show that joint inflammations can be induced by T cells only and that, after waning, reexposition to the original antigen can induce a flare-up reaction. The data suggest a central role of T cells in the induction and the exacerbations observed in rheumatoid arthritis.     

Differential effect of chromium compounds on the immune response of the African mouth breeder Oreochromis mossambicus (Peters)

The objective of this study was to investigate the effect of trivalent (chromic chloride) and hexavalent (potassium dichromate) forms of chromium in the African mouth breeder Oreochromis mossambicus (Peters), with reference to the humoral immune response and lymphoid cells/organs. The 96 h LD50 for hexavalent and trivalent chromium was found to be 75 and 1,000microg fish(-1), respectively. Groups of fishes were injected intraperitoneally with 10, 1, 0.1 and 0.01% LD50 hexavalent and trivalent forms of chromium and subsequently immunised with bovine serum albumin (5 mg in 0.2 ml physiological saline). Both forms of chromium suppressed the antibody response, with hexavalent chromium being more suppressive than trivalent chromium. Reduction in spleen weight, splenocyte number and the percentage of blood lymphocytes was observed following administration of both forms of chromium. The possible immunological mechanisms behind the differential suppression of the antibody response and the reduction in spleen weight, splenocyte and lymphocyte counts are discussed.     

Effects of carrageenan on immune responses. Studies on the macrophage dependency of various antigens after treatment with carrageenan.

Carrageenan, a sulfated polygalactose having macrophage toxic properties, elicited a marked suppression of IgM response to T cell-dependent antigens such as sheep red blood cells (SRBC), dinitrophenylated bovine serum gamma-globulin (DNP-BGG), and trinitrophenylated concanavalin A (TNP-Con A). In contrast, carrageenan did not inhibit antibody responses to such T cell-independent antigens as trinitrophenylated DEAE-dextran (TNP-DEAE-dextran), trinitrophenylated polyvinyl pyrrolidone(TNP-PVP), and trinitrophenylated Ficoll (TNP-Ficoll). Compared to total spleen cells, spleen cells from which macrophages had been removed by adhesion to plastic Petri dishes had less effect on the production of antibody against T cell-dependent antigens, but no change or a rather stimulated effect was observed in in vitro antibiody synthesis against T cell-independent antigens. These results strongly suggest that macrophages are involved in antibody responses to T cell-dependent antigens but not in those to T cell-independent antigens. However, the antibody response to trinitrophenylated lipopolysaccharide (TNP-LPS), a T cell-independent antigen, was inhibited by carrageenan treatment, suggesting that the response is macrophage dependent. Moreover, antibody response to higher doses of dinitrophenylated phytohemagglutinin (DNP-PHA), a T cell-dependent antigen, was shown to be macrophage independent by carrageenan treatment, although the antibody response to low doses of the antigen was macrophage dependent. Considering all these results, carrageenan treatment seems to be a very useful method to determine whether immune response to various antigens are macrophage dependent or not.     

Modulation of the IgE immune response to BSA by fragments of the antigen. I. Suppression by free fragments and by fragments conjugated to homologous gamma-globulin

Nonimmunogenic peptic fragments of bovine serum albumin (BSA), Fraction Ia, suppressed immune response to BSA in mice. Splenic T lymphocytes from mice treated with these fragments suppressed the anti-DNP response in irradiated mice reconstituted with DNP-BSA-primed cells, indicating carrier-specific suppression. The conjugate of Fraction Ia with mouse γ-globulin (MGG) was found to be an effective suppressive substance but it did not induce suppressor T cells. B cells from mice given Ia-MGG were unresponsive to BSA when transferred to irradiated recipients along with either normal or BSA-primed T cells. Thus, unresponsiveness to BSA was mediated by either T or B lymphocytes, depending whether the inducing substance was a free fragment of the antigen or fragments conjugated to homologous γ-globulin.     

Cell surface antigens and other characteristics of T cells regulating the antibody response to type III pneumococcal polysaccharide

The administration of a subimmunogenic dose of type III pneumococcal polysaccharide (SSS-III) produces an antigen-specific T cell-dependent phenomenon termed low-dose paralysis (immunologic unresponsiveness). This form of unresponsiveness can be transferred by spleen cells obtained 5 to 24 hr after priming, and the suppressive activity of the transferred cells is abolished by prior treatment with monoclonal anti-Lyt-2 and anti-I-J antibody in the presence of complement, indicating that suppression is mediated by a distinct subset of T cells (suppressor T cells). If primed spleen cells are transferred 24 to 72 hr after immunization with SSS-III, however, the resulting antibody response of immunized recipients is enhanced. Greater enhancement is noted when transferred cells, pretreated with monoclonal anti-Lyt-2 antibody plus complement to remove suppressor T cells, are used; such enhancement is attributed to amplifier T cells. These findings indicate suppressor T cells regulate the antibody response to SSS-III by influencing the expansion of SSS-III-specific clones of B cells as well as the expression of amplifier T cell activity; the latter causes B cells to proliferate further in response to SSS-III.     

Enhancement effects of BSA and linoleic acid on hybridoma cell growth and antibody production

The effects of linoleic acid and bovine serum albumin on hybridoma cell growth and antibody production were investigated. In dish cultivation, linoleic acid on its own promoted cell growth when used at concentrations below 50 mg L^–1, but strongly inhibited growth at a concentration of 100 mg L^–1 on more. However, linoleic acid bound to bovine serum albumin did not inhibit cell growth, even at a concentration as high as 100 mg L^–1. Also, linoleic acid did not affect the specific antibody production rate, with or without bovine serum albumin. In order to elucidate the enhancement of antibody production by bovine serum albumin, fractions were prepared by ultrafiltration (98% molecular weight cut-offs, 50,000 and 17,000) and the effects of the fractionation on antibody production were studied in batch cultivation. The high-molecular-weight fraction (50,000) promoted antibody production whereas the low-molecular-weight fraction (17,000) inhibited it. In continuous cultivation, the high-molecular-weight fraction was also found to enhance antibody production.     

Transition in the character of immunological memory in mice after immunization. II. Memory in T and B cell populations.

Teh immunological memory in antibody response of mice to bovine serum albumin (BSA) was investigated at the level of antibody-producing cells or their precursor B cells and thymus-dependent helper T cells. Spleen cells obtained from mice previously primed with alum-precipitated BSA at various times were transferred to irradiated syngeneic mice. Spleen cells from mice immunized 8 days or 64 days before presented a high degree of adoptive secondary response, whereas the adoptive response of cells from mice immunized 2 days previously was found to be inferior even to that of unprimed spleen cells. Primed spleen cells treated with anti-mouse thymocyte rabbit serum plus complement were supplemented with normal thymus cells and the restoration of the responsiveness was examined. It was suggested that the memory was carried mainly by T cells in the earlier phases of the immunological memory (2 days or 8 days after the primary immunization). On the other hand, the immunological memory in the B-cell population was shown to grow gradually toward the later phase (later than 40 days).     

In vivo suppression of the primary immune response by a species of low density serum lipoprotein.

An apparent subspecies of normal human serum low density lipoprotein (LDL-In) has been identified with suppressive activity for early or facilitating events of human lymphocyte mitogen and allogenic cells stimulation in vitro. This report describes the effects of in vivo administration of LDL-In on the mouse anti-SRBC immune response. Human LDL-In is not species specific and was capable of suppressing the in vivo mouse anti-sheep erythrocyte (SRBC) hemagglutination response by 88% after the administration of 500 to 600 mug LDL-In IV, whereas human serum high density lipoproteins and fibrinogen had no effect. Maximal suppression occurred only when LDL-In was injected 24 to 48 hr before antigen administration. Simultaneous or subsequent injection of LDL-In had no effect. The activity of LDL-In was influenced by antigen dose and maximal at low antigen doses. The number of splenic plaque-forming cells was also reduced indicating a suppression of the clonal expansion of primary B cells to antibody-secreting cells rather than only suppression of antibody synthesis by differentiated B cells and their progeny. These observations suggest the hypothesis that endogenous LDL-In could play an important immunoregulatory role in the maintenance of immune homeostasis and the "natural" suppression of non-productive lymphocyte proliferation.